The objective of this study is to investigate the epidemiology, pathogenesis, prevention, and therapy of infections of prosthetic heart valves in humans and experimental animals with an emphasis on infections caused by the bacterium, Staphylococcus epidermis. All patients with bacterial and fungal prosthetic valve infections will be prospectively studied. Patients' sera will be examined for bactericidal activity against selected pathogenic and saprophytic S. epidermidis isolates, and antibody to common S. epidermidis antigens will be sought. S. epidermidis isolates will be studied in vitro for antibiotic susceptibility, biochemical differentiation, and specific antigens. A rabbit model of S. epidermidis endocarditis will be used to study pathogenesis, prophylaxis, and antibiotic therapy.